Enabling Solar Hydrogen Production over Selenium: Surface State Passivation and Cocatalyst Decoration

As the first material ever used in a solid-state solar cell, selenium (Se) has outstanding merits of light absorption, carrier mobility, intrinsic environmental stability, and straightforward film preparation, making it an attractive light-absorbing semiconductor for photovoltaic applications. However, the exploration of selenium for photoelectrochemical (PEC) cells remains vastly unreported. Here, we successfully enable selenium as an absorber in the photocathode for solar hydrogen production. A rapid thermal annealing process is adopted to prepare a tetragonal Se film with a preferred [100] orientation. Using a thin layer of TiO2 buffer and platinum decoration, a photocurrent density up to −7.2 mA/cm2 is achieved over the optimal Se/TiO2/Pt photocathode at 0 VRHE under simulated one sun illumination. The roles of surface state passivation by TiO2 and cocatalyst decoration by Pt in charge separation and transfer were thoroughly investigated by capacitance–voltage profiling, photoassisted Kelvin probe force microscopy, photoelectrochemical impedance spectroscopy, and also transient photovoltage decay. Our work provides Se as a promising candidate for solar hydrogen production and also highlights the effectiveness of surface state passivation and cocatalyst decoration in the fabrication of efficient PEC devices.